|O.S. Goff, Sitting Bull (1881). Courtesy Library of Congress.|
This is a curious photograph of Sitting Bull (1831-1890), holding a pipe and wearing what seem to be goggles. You can find the original photo file online at the Library of Congress Prints and Photographs website. It was taken by Orlando Scott Goff on July 31, 1881, only about twelve days after the great Indian leader had returned to the US from Canada with his followers, in order to surrender.
But why is he wearing these goggles? As explained by James Welch in Killing Custer (New York: W.W. Norton, 2007, p. 258), he had a terrible eye infection at the time—
Sitting Bull certainly did not look well. He and his people had not eaten properly for three years. He was dressed in rags. He had a severe eye infection. He was demoralized.…[He was wearing] dirty pants and shirt, red paint on his face and a pair of smoked goggles shielding his infected eye…
Other people who were contemporaries with Sitting Bull also mention that he was wearing goggles when they met him. For example, this is a passage from Judson Elliot Walker, Campaigns of General Custer in the Northwest (Jenkins and Thomas, 1881, p. 90)—
He [Sitting Bull] wore a pair of green wire goggles, so we could not see his naked eyes, but it is said that he has a pair of as keen eagle eyes as ever was set between two high cheek bones on any red man in the aboriginal tribes.
And this is from J.W. Reading, "A Short Biography of Sitting Bull" in Locomotive Engineers Journal (1911), p. 219—
He [Sitting Bull] wore a pair of colored goggles, which served to partly hide the expression on his face, a thing that I regretted very much.
But maybe that isn't the (only) answer. I suggest that because it's just as easy to find eyewitness references to other Lakota Indians wearing colored goggles. When Laura Winthrop Johnson met a group of Lakota as early as 1875 (six years before this photograph of Sitting Bull), she reported that—
Several wore blue goggles—we knew not whether for use or beauty.
In addition, there are at least two photographs of the Oglala Lakota chief Red Cloud (1822-1909) in which he too is wearing goggles ("to protect his sensitive eyes"). Taken c.1891 by Clarence G. Morledge, those photographs are reproduced in Frank Henry Goodyear, Red Cloud: Photographs of a Lakota Chief.